Various object-detection systems and techniques exist. For example, Sound Navigation and Ranging (SONAR) is a technique that uses the propagation of sound waves to navigate or to communicate with or detect objects. SONAR may be used for acoustic location in both water and in the air, but has generally been supplanted by Radio Detection and Ranging (RADAR) for determining the range, speed, and so forth, of objects in the air. SONAR encompasses two primary types of ranging and detection schemes including passive SONAR, which involves listening for the sound made by vessels, and active SONAR, which involves emitting pulses of sounds and listening for echoes that are generated. While SONAR is a relatively inexpensive technology and is fairly accurate at short range, SONAR offers a relatively poor resolution compared to RADAR and other ranging technologies.
RADAR is an object detection system that makes use of radio waves to determine the range, altitude, speed, and so forth of objects. RADAR technology generally includes a transmitter that transmits pulses of radio waves or microwaves that bounce off of objects in their path. The objects return a portion of the wave's energy to a dish or antenna typically located in proximity to the transmitter. RADAR is not capable of directly determining position information between objects (e.g., an angular relationship between objects), which instead must be inferred from the range determination and an angle of the antenna. RADAR is a relatively expensive technology that provides better accuracy at longer ranges and better resolution than SONAR, for example.
Another sensing and ranging technology—Light Detection and Ranging (LIDAR)—is an optical remote sensing technology capable of measuring the distance to, or other properties of, a target, by illuminating the target with a pulse of light in the ultraviolet, visible, or near infrared spectrum from a Light Amplification by Stimulated Emission of Radiation (laser) source. LIDAR systems include both coherent and incoherent detection systems, each of which further encompasses two types of pulse models—micropulse and high energy systems. Micropulse systems use considerably less energy in the laser and are typically “eye-safe.” High energy systems are more commonly employed in conducting atmospheric research. LIDAR sensors mounted on mobile platforms (e.g., vehicles, satellites, etc.) require instrumentation to determine the absolute position and orientation of the sensor. Such instrumentation generally includes a Global Positioning System (GPS) receiver and an Inertial Measurement Unit (IMU). Similar to RADAR, LIDAR is only capable of determining a distance between objects; any determination of position information between objects must be inferred indirectly. While LIDAR generally offers better accuracy and higher resolution than other ranging technologies, such as SONAR and RADAR, LIDAR is also considerably more expensive to implement.